1. Field of the Invention
The present invention relates to a microtome having a motorized feed drive system for generating a relative movement between an object that is to be cut and a cutting knife. The drive system includes a control circuit and a pressure-sensitive sensor for detecting a defined position between the cutting knife and the object. The motorized feed drive system is switched via the control circuit when the sensor responds.
Modern microtomes are being equipped to an increasing extent with motorized drive means. The throughput of specimens to be sectioned is increased with a microtome of this kind. In automated microtomes, developments have also included equipping not only the cutting drive system for generating a movement between the object and the cutting knife, but also the system for feeding the object to the cutting knife (or the cutting knife to the object) with a motor. A microtome of this kind is depicted and described, for example, in WO 98 04 898 A1.
When an object is changed, for safety reasons the greatest possible spacing between the knife and the object is established. For that purpose, the feed drive system is moved into one end position. A relatively long distance must therefore be covered when an object to be sectioned first approaches the cutting knife. Since the distance between the object and the cutting knife is in most cases unknown, the displacement speed is kept correspondingly low.
For this reason it has become the practice, for example, to arrange in the displacement path sensors that switch off the feed drive system when they respond. A sensor of this kind that has a microswitch and a triggering tab joined thereto is known, for example, from DE 42 05 256 C2. Because there is little room in the feed area, an arrangement of this kind must be of very delicate configuration. This configuration has proven disadvantageous, however, since cut material is produced on the microtome during continuous cutting operation, and can clog the delicate arrangement. Reliable switching of the sensor during continuous operation therefore cannot be guaranteed.
2. Description of the Related Art
U.S. Pat. No. 4,691,151 discloses a control circuit for the feed drive system of a specimen mount on the cutting knife in which a distinction is made between coarse and fine modes. The feed movement for coarse operation is limited by a control device having a switch.
U.S. Pat. No. 3,667,330 also discloses a device for limiting the feed movement of the specimen holder. Here a switch is arranged on the microtome base.
The known limiting devices all suffer from the disadvantage that a mechanical switch that is triggered not by the specimen itself, but by the specimen holder or the moving component, is arranged in the movement path of the specimen holder or of the moving component. The size of the object being cut is not taken into consideration with these devices, however, so that in all these cases the switch must operate with a greater or lesser safety distance between the object and the cutting knife. With these devices, an exact approach can be made only manually. The known devices make no provision for correlating the cutting plane with the surface of the object.
It is therefore one object of the present invention to provide an improved microtome.
A further object of the invention is to provide a microtome having a motorized feed drive system that permits an unequivocal correlation between the position of the cutting plane and the object.
In accomplishing the foregoing objects, there has been provided in accordance with the present invention a microtome comprising a cutting knife and an object holder that are movable relative to one another; a motorized feed drive system for generating a relative movement between the object holder for holding an object that is to be cut and the cutting knife. The drive system includes a control circuit and a pressure-sensitive sensor for detecting a position between the cutting knife and the object, wherein the motorized feed drive system is activated by the control circuit in response to signals from the sensor, wherein the sensor comprises a sensor surface that is at least as large as the surface of the object, and the sensor surface is arranged parallel to a cutting plane defined by the cutting knife.
Further objects, features and advantages of the present invention will become apparent from the detailed description of preferred embodiments that follows, when considered with the accompanying figures of drawings.